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Abstract

Polymer-derived ceramics (PDCs) are exceptional ultra-high temperature and stable multifunctional class of materials that can be synthesized from a polymer precursor through thermal decomposition. The presented research focuses on 1-D nanofibers, 2-D films and 3-D bulk, carbon-rich silicon carbon nitride (SiCN) ceramics. 1-D nanofibers were prepared via electrospinning for light weight, flame retardant and conductive applications. The commercially available CerasetTM VL20, a liquid cyclosilazane pre-ceramic precursor, was mixed with polyacrylonitrile (PAN) in order to make the cyclosilazane electrospinnable. Carbon-rich PDC nanofibers were fabricated by electrospinning various ratios of PAN/cyclosilazane solutions followed by pyrolysis. Surface morphology of the electro spun nanofibers characterized by SEM show PDC nano?bers with diameters ranging from 100-300 nm. Also, thermal stability towards oxidation showed a 10% mass loss at 623°C. 2-D carbon/SiCN films were produced by drop-casting a mixture of PAN/cyclosilazane onto a glass slide followed by pyrolysis of the film. Samples ranging from 10:1 to 1:10 PAN:cyclosilazane were made by dissolving the solutes into DMF to produce solutions ranging from 1% to 12% by weight. Green, heat-stabilized, and pyrolyzed 8% films were examined with FTIR to monitor the change in chemical structure at each step of the ceramization. SEM shows that high PAN samples produced films with ceramic embedded spheroid components in a carbon matrix, while high cyclosilazane samples produced carbon embedded spheroid. Finally, this research focuses on the challenge of making fully dense, 3-D bulk PDCs materials. Here we present a composite of SiCN with reduced graphene oxide (rGO) aerogels as a route for fully dense bulk PDCs. Incorporation of the rGO aerogel matrix into the SiCN has its pros and cons. While it lowers the strength of the composite, it allows for fabrication of large bulk samples and an increase in the electrical conductivity of the PDC. The morphology, mechanical, electrical properties and thermal conductivity of graphene-SiCN composite with varying rGO aerogel loading (0.3-2.4%) is presented. The high temperature stability, high electrical conductivity and low thermal conductivity of these composites make them excellent candidates for thermoelectric applications. Generally, carbon-rich SiCN composites with improved thermal and electrical properties are of great importance to the aerospace and electronics industries due to their expected harsh operating environments.

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